<template>
  <!-- @scroll为scroll组件里面的$emit的派生事件 -->
    <scroll
      class="listview"
      :data="data"
      ref="listview"
      :listenScroll="listenScroll"
      :probeType="this.probeType"
      @scroll="scroll"
    >
      <ul>
        <li
          class="list-group"
          v-for="(group, index) in data"
          :key="index"
          ref="listGroup"
        >
          <h2 class="list-group-title" :ref="group.title">{{group.title}}</h2>
          <ul>
            <li
              class="list-group-item"
              v-for="item in group.items"
              :key="item.id"
              @click="selectItem(item)"
            >
              <img class="avatar" v-lazy="item.avatar" alt="">
              <span class="name">{{item.name}}</span>
            </li>
          </ul>
        </li>
      </ul>
      <!-- touchstart和touchmove这些事情都是由better-scroll封装好的 -->
      <div
        class="list-shortcut"
        @touchstart="onShortcutTouchStart"
        @touchmove.stop.prevent="onShortcutTouchMove"
      >
        <ul>
          <li
            class="item"
            :class="{'current':currentIndex === index}"
            v-for="(item, index) in shortcutList"
            :data-index="index"
            :key="index"
          >
            {{item}}
          </li>
        </ul>
      </div>
      <div class="list-fixed" v-show="fixedTitle" ref="fixed">
        <h1 class="fixed-title">{{fixedTitle}}</h1>
      </div>
      <div v-show="!data.length" class="loading-container">
        <loading></loading>
      </div>
    </scroll>
</template>

<script>
import Scroll from 'base/scroll/scroll'
import Loading from 'base/loading/loading'
import {getData} from 'common/js/dom'

const ANCHOR_HEIGHT = 18
const TITLE_HEIGHT = 30

export default {
  name: 'listview',
  props: {
    data: {
      type: Array
    }
  },
  data () {
    return {
      scrollY: -1,
      currentIndex: 0
    }
  },
  components: {
    Scroll,
    Loading
  },
  computed: {
    shortcutList () {
      return this.data.map((group) => {
        return group.title.substr(0, 1)
      })
    },
    fixedTitle () {
      if (this.scrollY > 0) {
        return ''
      }
      return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
    }
    /*
    currentIndex () {
      for (let i = 0; i < this.listHeight.length; i++) {
        let Height1 = this.listHeight[i]
        let Height2 = this.listHeight[i + 1]
        if (!Height2 || (this.scrollY >= Height1 && this.scrollY < Height1)) {
          return i
        }
      }
    }
    */
  },
  created () {
    this.touch = {}
    this.listenScroll = true
    this.listHeight = []
    this.probeType = 3
  },
  methods: {
    selectItem (item) {
      // 把点击事件的item派发出去
      this.$emit('select', item)
    },
    onShortcutTouchStart (e) {
      let anchorIndex = getData(e.target, 'index')
      /* 就是你第一根手指的位置 */
      let firstTouch = e.touches[0]
      this.touch.y1 = firstTouch.pageY
      /* 记录下第一个锚点所点击的位置 */
      this.touch.anchorIndex = anchorIndex
      this._scrollTo(anchorIndex)
      /*
      this._scrollTo(anchorIndex)
      console.log(e.target)
      */
    },
    onShortcutTouchMove (e) {
      let firstTouch = e.touches[0]
      this.touch.y2 = firstTouch.pageY
      /* |0相当于math.floor */
      let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
      let anchorIndex = parseInt(this.touch.anchorIndex) + delta
      this._scrollTo(anchorIndex)
    },
    // 刷新
    refresh () {
      this.$refs.listview.refresh()
    },
    scroll (pos) {
      this.scrollY = pos.y
      // console.log(this.scrollY)
    },
    _scrollTo (index) {
      /* 侧边栏A-Z的上下为了美观，多了一点东西，设置为null时候的样式 */
      if (!index && index !== 0) {
        return
      }
      if (index < 0) {
        index = 0
      } else if (index > this.listHeight.length - 2) {
        index = this.listHeight.length - 2
      }
      this.scrollY = -this.listHeight[index]
      this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 300)
    },
    _calculateHeight () {
      this.listHeight = []
      const list = this.$refs.listGroup
      let height = 0
      this.listHeight.push(height)
      for (let i = 0; i < list.length; i++) {
        let item = list[i]
        height += item.clientHeight
        this.listHeight.push(height)
      }
      console.log(this.listHeight)
    }
  },
  watch: {
    data () {
      setTimeout(() => {
        this._calculateHeight()
      }, 20)
    },
    scrollY (newY) {
      const listHeight = this.listHeight
      // 当滚动到顶部，newY > 0
      if (newY > 0) {
        this.currentIndex = 0
        return
      }
      // 当滚动到中部的时候
      for (let i = 0; i < listHeight.length - 1; i++) {
        let height1 = listHeight[i]
        let height2 = listHeight[i + 1]
        if (-newY >= height1 && -newY < height2) {
          this.currentIndex = i
          this.diff = height2 + newY
          return
        }
      }
      // 当滚动到底部,且-newY大于最后一个元素的上限
      this.currentIndex = listHeight.length - 2
    },
    diff (newVal) {
      let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
      if (this.fixedTop === fixedTop) {
        return
      }
      this.fixedTop = fixedTop
      this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
    }
  }
}
</script>

<style lang="stylus" scoped>
  @import "~common/stylus/variable";
  .listview
    position relative
    width 100%
    height 100%
    overflow hidden
    background $color-background
    .list-group
      padding-bottom 30px
      .list-group-title
        height 30px
        line-height 30px
        padding-left 20px
        font-size $font-size-small
        color $color-text-l
        background $color-highlight-background
      .list-group-item
        //居中对齐弹性盒（）flex+align-items
        display flex
        align-items center
        padding 20px 0 0 30px
        .avatar
          width 50px
          height 50px
          border-radius 50%
        .name
          margin-left 20px
          color $color-text-l
          font-size $font-size-medium
    .list-shortcut
      z-index 30
      position absolute
      right 0
      top 50%
      transform translateY(-50%)
      width 20px
      padding 20px 0
      border-radius 10px
      text-align center
      background $color-background-d
      .item
        padding 3px
        line-height 1
        color $color-text-l
        font-size $font-size-small
        &.current
          color $color-theme
    .list-fixed
      position absolute
      top 0
      left 0
      width 100%
      .fixed-title
        height 30px
        line-height 30px
        padding-left 20px
        font-size $font-size-small
        color $color-text-l
        background $color-highlight-background
</style>
